a) Field of the Invention
The present invention relates to an internal combustion engine in which a variable valve timing controlling apparatus is installed which varies open and closure timings of one or both of an intake valve or intake valves and an exhaust valve or exhaust valves according to an engine driving condition.
b) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 9-280017 published on Oct. 28, 1997 exemplifies a first previously proposed variable valve timing controlling apparatus of a vane type.
The first previously proposed variable valve timing controlling apparatus of the vane type disclosed in the above-identified Japanese Patent Application First Publication includes a timing pulley having a cylindrical housing in which a vane fixed to an end of a camshaft is rotatably housed and an advance-angle hydraulic pressure chamber and a retardation-angle hydraulic pressure chamber defined between two approximately trapezoid shaped partitioning wall sections and two blade portions. The cylindrical housing of the timing pulley has an opening enclosed by a front cover and a rear cover. The trapezoid shaped partitioning wall sections are located on an inner peripheral surface of the housing and mutually projected toward their inner directions from a radial direction thereof.
Then, a hydraulic pressure (working oil pressure) is supplied or exhausted (drained) through a hydraulic pressure circuit into or from each of the advance-angle hydraulic pressure chamber and the retardation-angle hydraulic pressure chamber according to an engine driving condition so that the related hydraulic pressure causes the vane to rotate in either the normal direction or reverse direction. As the result, a relative rotational phase between the timing pulley and the camshaft is varied to enable the variation of open-and-closure timings of an intake valve of the engine.
However, in the first previously proposed variable valve timing controlling apparatus described above, each hydraulic passage in a hydraulic circuit to supply the hydraulic pressure into either the advance angle hydraulic pressure chamber or the retardation angle hydraulic pressure chamber is communicated with a main gallery which supplies a lubricating oil into each slide portion of the engine, viz, in an open circuit configuration. A positive or negative revolution variation torque is, hence, developed so that a rotation of the vane becomes unstable. That is to say, it is well known that a rotation variation (fluctuating) torque (in a form of an alternating torque) in a normal direction or reverse direction due to a presence in a spring force of a valve spring disposed along a stem of each engine valve is developed during an engine operation.
If a large rotation variation torque is acted upon the camshaft during a rotational drive of the vane in an advance or retardation angle side, the vane is rotated in the advance angle side progressively repeating the normal rotation and the reverse rotation toward the advance angle side or the retardation angle side (as denoted by a broken line of FIG. 8B) since the hydraulic pressure supplied to the advance angle hydraulic chamber is pressed against a reaction force exerted by the normal directional variation torque and which is acted upon in an opposite direction to the rotation direction. Hence, since the camshaft also carries out the relative rotation to the timing pulley repeating the normal rotation and the reverse rotation, a control response characteristic of the valve open-and-closure timing control for the intake valve is reduced.
Especially, when the vane is rotated in the advance-angle direction, a quick switching action is demanded since the vane advance-angle direction rotation means generally the switching from an engine idling state to a normal driving state. However, during a transition from a low-engine-speed region to a middle-engine-speed region, it becomes easy for the vane to be reversed due to a reaction force of the rotation variation torque.
A Japanese Patent Application First Publication No. Heisei 8-121123 published on May 14, 1996 exemplifies a second previously proposed variable valve timing controlling apparatus of the vane type.
In the second previously proposed variable valve timing controlling apparatus, a pilot-type check valve is installed which includes a check valve and a pilot valve, both valves being extended in an inside portion of the vane and being operated to limit a reverse flow of the drive hydraulic pressure supplied to either the advance-angle or the retardation-angle hydraulic chamber within the hydraulic passage so as to prevent the reverse rotation of the vane due to the rotation variation torque.